In one form of vacuum bag molding, prepreg sheet material is laid up on a mold tool. A flexible vacuum bag is then placed over the layup and the edges of the bag are sealed to the mold tool. The mold tool may be heated and a vacuum is drawn within the bag that results in the surrounding atmospheric pressure applying pressure to the layup. In some cases, the mold is placed in an autoclave that applies both heat and external pressure, adding to the force of the atmospheric pressure applied to the bag. It may be desirable to measure the pressure that is applied at various locations over the layup since these local pressures may have an affect on the porosity, and thus the quality of the cured composite part.
Current systems for monitoring molding pressures, particularly those where the layup is processed in an autoclave, employ one or more vacuum hoses that are connected between the autoclave shell or wall, and the vacuum bag. The hoses are connected to pressure/vacuum transducers which are located outside of the autoclave. This technique measures only vacuum bag pressure, and does not sense the hydrostatic pressure of the resin which can be important in monitoring and controlling the process. Furthermore, because the vacuum hoses are relatively bulky and expensive, only a limited number of transducers are used to monitor the process, thus limiting the amount of information that can be gathered. Moreover, the use of long hoses to connect remote transducers to the layup may affect measurements in unpredictable ways.
Accordingly, there is a need for a system for collecting vacuum and pressure data that eliminates the need for long connecting hoses by using multiple in-situ sensors located on or immediately near the vacuum bag to collect the data. Further, there is a need for a system of the type mentioned above that is highly flexible and allows measurement of at least some parameters before a part layup is loaded into the autoclave and/or after the part layup has been removed from the autoclave.